Is this expression, "the one function", grammatical in formal cases?

[shiqangpan]

It seems that the lecturer is saying

Code: Select all

https://youtu.be/p4wlQnZcBrg?t=3360

how are we going to find the one function we're after

I guess he is emphasizing there is only one function we're after while there are two many possible options.

My question is,

Is this expression grammatical in formal cases such as a text book?

[Josef Essberger]

I agree that's what he's saying.

And it's perfectly grammatical even in formal settings.